This invention is generally directed to positively charged toner compositions, and more specifically, the present invention is directed to positively charged toner compositions containing a low molecular weight wax such as polyethylene or polypropylene, and a charge enhancing additive. In one embodiment, the present invention is directed to a toner composition comprised of one or more polymeric resins exhibiting peak value molecular weights in the molecular weight regions of 5.times.10.sup.3 to 8.times.10.sup.4, and 10.sup.5 to 2.times.10.sup.6, respectively, as measured by gel permeation chromotography (GPC); a low molecular weight wax component pigment particle; and a charging enhancing additive. These compositions are particularly useful for permitting the development of images, including colored images in electrophotographic imaging processes wherein an offset preventing liquid, such as a silicon oil, is not required.
Developer compositions with additives, which impart a positive charge to the toner resin, are well known. Thus, for example, there are described in U.S. Pat. No. 2,986,521 reversal developer compositions comprised of toner resin particles coated with finely divided colloidal silica. According to the disclosure of this patent, the development of electrostatic latent images on negatively charged surfaces is accomplished by applying a developer composition having a positively charged triboelectric relationship with respect to the colloidal silica. Additionally, in U.S. Pat. No. 3,893,935 there is described the utilization of certain quaternary ammonium salts as charge control agents for electrostatic toner compositions. There are also described in U.S. Pat. No. 4,298,672 positively charged toner compositions with resin particles and pigment particles; and as a charge enhancing additive alkyl pyridinium compounds and their hydrates, inclusive of cetyl pyridinium chloride.
In addition, positively charged colored toner compositions are illustrated in U.S. Pat. No. 4,604,338, the disclosure of which is totally incorporated herein by reference, which compositions are comprised of first resin particles; second crosslinked resin particles; colored pigment particles excluding black, and selected from the group consisting of, for example, cyan, magenta, yellow, blue, red, and brown; a low molecular weight wax; and a charge enhancing additive selected from the group consisting of alkyl pyridinium halides, organic sulfonate compositions, organic sulfate compositions, distearyl dimethyl ammonium methyl sulfate, behenyl trimethyl ammonium methyl sulfate, and distearyl methyl ethyl ammonium ethyl sulfate. Furthermore, illustrated in U.S. Pat. No. 4,556,624, the disclosure of which is totally incorporated herein by reference, are toner compositions with crosslinked resins, and low molecular weight wax components, as well as charge enhancing additives. The aforementioned compositions are useful in imaging systems wherein release oils such as silicones are not required.
There is illustrated in U.S. Pat. No. 4,564,573 a toner composition that includes as an essential component a binder resin comprised of at least 60 percent by weight of a styrene butadiene copolymer, which contains a component A with a molecular weight of at least 100,000; and wherein said component A contains a component B with a molecular weight of at least 50,000, reference column 3, at line 50. Additive such as coloring agents and charge control agents may be incorporated into the toner compositions illustrated in this patent. Also of interest is the disclosure in column 3, line 62, and continuing on to column 4. According to the disclosure of this patent, the toners illustrated have adequate flowability, and noncoagulation properties, and are capable of forming superior visable images with heat fixing processes. Moreover, there are illustrated in U.S. Pat. No. 4,486,524 toner compositions comprised of resin particles containing at least 60 percent by weight of specific polymers selected from, for example, copolymers of aromatic vinyl monomers with at least one other alpha-methylene aliphatic monocarboxylic acid ester, which polymer has a weight average molecular weight number average molecular weight ratio of from 3.5 to 40, and wherein the number average molecular weight is between 2,000 and 30,000. This patent also discloses a toner composition wherein the resin selected is preferably comprised of a low molecular weight polymer, for example molecular weight between 100,000 and 500,000, and a low molecular weight polymer with a molecular weight of not more than 30,000, reference column 4, lines 1 to 6, which toner can be utilized for preventing offsetting, reference column 5, lines 34 to 36. This toner may also include therein charge controlling agents and plasticizers, reference column 14, lines 9 to 12.
Of particular interest with respect to the subject matter of the present application is U.S. Pat. No. 4,499,168, the disclosure of which is totally incorporated herein by reference, which illustrates developer powders comprising one or more vinyl type copolymers exhibiting a peak value molecular weight in each of the molecular weight regions of 5.times.10.sup.3 to 8.times.10.sup.4, and 10.sup.5 to 2.times.10.sup.6, respectively, as measured by gel permeation chromotography, and an ethylene type olefin homo, or copolymer with a melt viscosity of for, example, 10 centipoises at 14.degree. C. The aforementioned compositions are useful in xerographic imaging systems wherein fusing is accomplished with no silicone oils, reference column 3, line 54. Specific embodiments of toner compositions illustrated in this patent are described in column 4, line 14, and continuing on to column 6, line 68. Moreover, as indicated in column 7, line 64, suitable type ethylene olefins that may be selected are polyethylene, polypropylene, and the like. In addition, in column 7, line 15, it is stated that the toner selected for the present invention can have incorporated therein various additive materials for the purpose of coloring, charge control, and the like. Additives described include carbon black, iron black, graphite, nigrosine, metal complexes of monoazo dyes, and others, reference column 7, line 18, and continuing on to line 33. This patent is silent, however, with respect to formulating positively charged toner compositions, especially containing specific charge enhancing additives, the subject matter of the invention of the present application.
With further respect to the prior art, it is know that to substantially eliminate offsetting, and more specifically for the purpose of preventing adhesion of the toner particles to the surface of the fixing roller there can be selected certain types of rollers, the surface of which may be covered with a thin film of an offset preventing liquid such as a silicone oil. These oils are highly effective, however, the apparatus within which they are incorporated is complicated and costly since, for example, a means for feeding the oil is required. Also, not only do the silicone oils emit an undesirable odor, they can deposit on machine components causing toner particles to adhere to the oils. An accumulation of toner particles on machine components is troublesome in that the image quality is adversely effected, and further these components must be periodically cleaned and/or replaced adding to the maintenance costs thereof. The aforementioned offsetting problems can be substantially eliminated with the black and magnetic toner compositions as disclosed in U.S. Pat. No. 4,460,672. This patent, the disclosure of which is totally incorporated herein by reference, illustrates positively charged toner compositions comprised of resin particles, pigment particles, a low molecular weight wax material, and a charge enhancing additive. More specifically, in one embodiment the U.S. Pat. No. 4,460,672 discloses a positively charged black toner composition comprised of resin particles containing polyester resins, styrene butadiene resins, or styrene butyl methacrylate resins; pigment particles; a low molecular weight waxy composition, such as a low molecular weight polyethylene or polypropylene; and a charge enhancing additive selected from the group consisting of alkyl pyridinium halides, organic sulfonate additives and organic sulfate additives. Also, there is described in copending application U.S. Ser. No. 655,381, entitled Toner Compositions With Crosslinked Resins and Low Molecular Weight Waxes, the disclosure of which is totally incorporated herein by reference, positively charged electrostatic toner compositions comprised of a polyblend mixture of a crosslinked copolymer composition, a second thermoplastic polymer, pigment particles, a charge enhancing additive, and a wax component. The aforementioned compositions are useful for affecting the development of images wherein offset preventing liquid such as a silicone oil is not required.
Accordingly, there is a need for positively charged toner compositions which can be selected for incorporation into electrostatographic imaging systems wherein offset preventing fluids such as silicone oils are not required. Additionally, there is a need for toner compositions that simultaneously possess acceptable developing characteristics, and excellent imaging fixing properties. There is also a need for positively charged toner compositions wherein offsetting of the toner image to the fuser roll is substantially eliminated. Additionally, there is a need for toner compositions wherein the toner is readily releasable from the carrier particles, the surface of the imaging member, and cleaning blades; and further a need for toner compositions that avoid and coagulation, and possess excellent fluidity and durability. There is also a need for positively charged toner compositions wherein imaging can be accomplished with coated hard fuser rolls, and substantially no offsetting results; and wherein layered imaging members are selected.